Products in the form of aerated dispersions (e.g. gas-in-water dispersions) are known, such as, for example, foams such as mousse products for styling the hair, as well as whipped cream and other food products that are dispensable from an aerosol can. Such products, however, are known to have poor stability, in particular at room temperature.
Past attempts to formulate stable products have had the drawback that the product is affected by the addition of surfactants, polymers, and changes in temperature and/or pH. Other past methods for preparing and stabilizing formulated products utilize components that are toxic and/or produce by-products that can present health hazards and/or introduce prohibitive cost constraints to remove or neutralize them. Additionally, some aerated products are proposed in aerosol cans that simultaneously inject gas and solution, or that must be prepared and kept under frozen conditions to remain stable.
Further problems with the current methods for generating aerated products with particles at the gas-solution interface is that they concern foams and not gas-phase dispersions—that is, the systems have gas-phase volume fractions greater than 64%. In these systems the individual bubbles touch and stick together which makes it difficult to subsequently re-disperse the gas bubble into solution. Furthermore, only hydrophobic particles can be used to achieve even moderate stability.
U.S. Pat. No. 3,661,602 discloses a method of stabilizing aqueous foams that incorporates certain silanes to prepare a stable, rigid foam that is “set” upon drying. U.S. Pat. No. 3,725,095 discloses a method of stabilizing aqueous foams with a combination of a cationic surfactant, colloidal silica particles, and an alkaline ionic silicate. The foams in both of these disclosures, however, isolate the gas bubbles in a solid, continuous matrix.
In addition to avoiding the above-mentioned drawbacks, there is also a desire in certain industries, such as, for example, the food, cosmetic, and consumer chemical (e.g. household product) industries, to prepare products that have certain properties, such as the ability to be further diluted, for instance, which the two references mentioned do not provide.
Thus, there remains a need for methods to prepare gas-in-water dispersions that provide the desired properties and which can be used in a variety of applications and industries, while providing increased stability of the dispersion and the formulated product.